This invention relates to a sealing clip comprised of a wire section for bags, film tubes or the like, having a pre-bent clip base and two clip legs adjoining the latter on both sides. The invention furthermore relates to a wire section for the sealing clip and to a matrix having two sliding grooves for closing the sealing clip.
Simple sealing clips consisting of a wire section can be produced in that an endless wire is supplied to a sealing machine, a portion is cut off from the wire in the sealing machine, and the wire section is then for instance bent around a bag neck to be closed. It is likewise known to supply to a sealing machine not an endless wire, but wire sections already cut through. The wire sections may be straight or prebent to form a U. For magazining purposes, these wire sections are generally fixed one beside the other on a carrier strap, so that they form a magazine strand. The advantage of such sealing clips formed of a wire section resides in the easy manufacture of these sealing clips. The tightness of the closures which can be achieved with the known sealing clips formed of a wire section is, however, not satisfactory.
As a tool for closing the above-mentioned sealing clips there are usually used sealing machines which have a stamp and a matrix. The sealing clip pre-bent to form a U is first of all transferred from a magazine to the stamp and non-rotatingly guided. Subsequently, stamp and matrix are moved towards each other. During this movement, the sealing clip surrounds the packaging material gathered to form a neck. Then, the free ends of the legs of the sealing clip are the first to reach the matrix and in the course of the further movement are guided by sliding grooves in the matrix. In the process, the legs of the sealing clip are plastically deformed, so that there is finally obtained a more or less circularly closed sealing clip.
There are known matrixes which have two semicircular sliding grooves arranged parallel to each other. The main plane of the two sliding grooves is slightly inclined with respect to the main plane of the sealing clip, so that each sliding groove has an inlet point which lies in the main plane of the sealing clip. Main plane is understood to be that plane in which extends the center line of a sliding groove or the sealing clip. When the sealing clip guided by a stamp is moved towards the matrix for closure, each of the free leg ends enters one of the sliding grooves at a respective inlet point and is guided by the same on a helical path produced by the inclination of the sliding grooves. As a result, the two free ends of the sealing clip slide past each other during closure, so that upon closure they laterally overlap each other and rest against each other in parallel.
It is the object underlying the invention to provide a sealing clip comprised of a wire section, with which tighter closures can be achieved than with the sealing clips known so far.
In accordance with the invention, the solution of this object consists in a sealing clip as described above, which is characterized in that during closure the two clip legs taper constantly from their clip base ends to their free ends. This is based on the knowledge that during closure a sealing clip made of wire with a uniform cross-section always bends particularly in the vicinity of the arc sections between the legs and the clip base, because there the bending load is largest. Therefore, sealing clips consisting of a wire section of uniform cross-section never take on the circular shape ideal for tight closures. Since the wire cross-section of the inventive sealing clip tapers towards the legs, there is a much more uniform distribution of the bending load over the entire length of the legs, so that during closure the sealing clip approximately takes on the ideal circular shape.
Preferably, the clip base and the clip legs of the sealing clip have a round cross-section. Such sealing clip can be produced easily and inexpensively from a piece of round wire, which is partly stretched, so that the tapering legs are obtained.
In a preferred embodiment of the sealing clip the clip base has been preformed to form a circular arc. Preforming the clip base to form a circular arc promotes the approach of the sealing clip to the ideal circular shape during closure.
There is furthermore preferred a sealing clip which has a projection at the outer radius of the clip base. By means of such projection the sealing clip can be non-rotatingly guided in the stamp during closure.
The solution of the object underlying the invention also comprises a wire section for the inventive sealing clips which is characterized in that the wire section tapers constantly towards both ends. Such wire section solves the inventive object in particular in conjunction with those machines to which straight, not pre-bent wire sections are supplied. In this case, the individual wire sections are only pre-bent to form a U in the sealing machine (DE 41 20 440).
In the case of a straight wire section it is particularly advantageous when the cross-section of the wire section decreases constantly from the middle of the wire section to both ends, so that the wire section already tapers towards both sides in the vicinity of its future clip base. In this way, it is already during preforming that the wire section is subjected to a uniform bending load in the vicinity of the clip base, so that it easily takes on the shape of a circular arc.